EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1120 PM EDT SAT APR 08 2017 VALID 12Z WED APR 12 2017 - 12Z SUN APR 16 2017 PATTERN OVERVIEW... DURING THE UPCOMING MEDIUM RANGE PERIOD, WED-SUN, A MEAN LONGWAVE TROUGH IS EXPECTED TO PREVAIL ALONG THE WEST COAST, WHILE PERIODICALLY EJECTING PORTIONS OF THE TROUGH EASTWARD, POSSIBLY ALLOWING THE LONGWAVE TROUGH TO WEAKEN AND DRIFT NORTHWARD WITH TIME. MEANWHILE, COLD FRONTS ACCOMPANYING THE LEADING EDGES OF THE TROUGH WILL PROGRESS QUICKLY ACROSS THE CONUS BEFORE SLOWING AND WEAKENING WHILE ENCOUNTERING THE LONGWAVE RIDGE OVER THE SOUTHEAST. MODEL PREFERENCES... THE LAST 2 RUNS OF THE GFS BECOME UNREPRESENTATIVE OF THE MODEL CONSENSUS BY BECOMING TOO QUICK WITH THE LEADING EDGE OF THE TROUGH ENTERING THE WEST COAST BY DAY 4/THU AS WELL AS TOO FAST WITH A SHORTWAVE TROUGH OVER THE GREAT LAKES. THUS, THESE SOLUTIONS WERE QUICKLY ABANDONED FOR MODEL CHOICES. MEANWHILE, THE 12Z ECMWF/12Z UKMET/12Z CANADIAN ARE WELL ALIGNED WITH THE ENSEMBLE MEANS FOR MOST SYSTEMS THROUGH DAY 5/FRI, BEFORE SWITCHING A BLEND OF THE ENSEMBLE MEANS AND ABOUT 25 PERCENT OF THE 12Z OPERATIONAL ECMWF FOR DETAIL FOR DAYS 6-7/SAT-SUN AS THE MODEL SPREAD INCREASES. CONFIDENCE IN THE TIMING AND PLACEMENT OF INDIVIDUAL SYSTEMS IS ABOUT AVERAGE THROUGH DAY 5 BEFORE BECOMING BELOW AVERAGE. SENSIBLE WEATHER HIGHLIGHTS... PERIODS OF MODERATE TO POSSIBLY HEAVY PRECIPITATION AND COOLER TEMPERATURES WILL ACCOMPANY THE LEADING EDGE OF THE LONGWAVE TROUGH AS IT PROGRESSES ACROSS THE WEST COAST NEXT THURSDAY AND FRIDAY BEFORE TEMPERATURES POSSIBLY REBOUND AND PRECIPITATION BECOMES MORE SCATTERED AS THE BASE OF THE TROUGH POSSIBLY REACHES THE COAST, DRIFTS NORTHWARD, AND WEAKENS. MEANWHILE, CONVECTION CAN BE EXPECTED FROM THE SOUTHERN PLAINS TOWARD THE GREAT LAKES AS COLD FRONT PROGRESS EASTWARD BEFORE WEAKENING, WHILE GENERALLY WARM AND DRY CONDITIONS PREVAIL ACROSS THE SOUTHEAST BENEATH THE UPPER RIDGE. JAMES